This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications JP2002-348003 filed Nov. 29, 2002 and JP2002-21349 filed on Jan. 30, 2002, the entire contents of which are incorporated herein by reference.
The present invention relates to a high-pressure discharge lamp having a translucent ceramic discharge vessel, and a luminaire using such a discharge lamp.
Developments for high-pressure discharge lamps have been widely continued since high-pressure discharge lamps are characterized by properties of high efficiency and long life of time.
Especially, a compact single-based metal halide lamp with a rated lamp wattage of about 10-30 W have been developed in recent-years as lighting sources for halogen lamps such as compact single-based high-pressure discharge lamps and headlights.
Such a compact single-based metal halide lamp is known in the conventional arts, JP-10-284004-A, JP-10-83796-A, JP-2001-76677-A, etc.
Such a conventional compact single-based metal halide lamp typically comprises, a translucent ceramic discharge vessel having a pair of cylindrical portions formed in communicating with a swollen portion at its opposite sides, the cylindrical portions respectively having an inner diameter shorter than that of the swollen portion, a pair of metal tubes each fit in the cylindrical portion, a pair of fusible metal plugs each closing the open end of the metal tube thereby an electrode supported to the metal plug facing the interior of the swollen portion, and ionizing filling such as halide, mercury, or rare gas filled in the discharge vessel.
Such a conventional compact single-based metal halide lamp has a lamp efficiency higher than halogen lamps by three to four times. Moreover, the size is remarkably smaller than compact single-based fluorescent lamps. Therefore, the compact single-based metal halide lamp can be used as a point source, and thus it is supposed as an arc tube for novel lighting system other than compact single-based high-pressure discharge lamps and headlights.
However, such a conventional compact single-based metal halide lamp still has a problem of spoiling the reliability on the lamp life time by leaks taking place at the sealing portion due to an incomplete fitting of the fusible metal plug to the open end of the metal tube and a difference between coefficient-of-thermal-expansions of the fusible metal plug and the metal tube.
Although such a problem of leaks occurring at the sealing portion could be avoided by, for example, lengthening the metal tube so as that the temperature of the sealing portion of the metal tube. However, there still remains a problem of that the size of the discharge lamp cannot be reduced.
In order to solve the above problems, an object of the present invention is to provide a high-pressure discharge lamp with less leaks of ionizing filling and thus capable of maintaining a high reliability for a long time and a luminaire equipped with such a high-pressure discharge lamp. Another object of the present invention is to provide a fixture, which having heat conductive member cools the fluorescent lamp effectively.
A translucent ceramic discharge vessel according to the one aspect of the invention comprises, a translucent ceramic discharge vessel having a swollen portion defining a discharge space and a pair of cylindrical portions formed in communicating with the swollen portion and extending from the swollen portion in the opposite directions with each other, metal tubes each having a outer diameter D and fit with its one end on the cylindrical portion, a pair of fusible metal plugs each plugged in the outer end of the metal tube, the fusible metal plug sealing the discharge vessel by being fused to the inner surface of the metal tube for a specified height T from the outer end of the metal plug, a pair of electrode systems each supported its one and to the fusible metal plug and facing the interior of swollen portion with its other end and ionizing filling filled in the discharge vessel, wherein the ratio T/D of the height T concerning the fusible metal plug and the diameter D satisfies the following equation.
0.40xe2x89xa6T/Dxe2x89xa60.95 
In this application, some definitions and their technical meanings are presented for following specific terms, unless otherwise specified.
A discharge vessel defining discharge space has a swollen portion in a shape of spherical, oval, ellipse or cylindrical, and a pair of cylindrical portions extending from the swollen portion in the opposite directions with each other. The swollen portion and the pair of cylindrical portions may be formed in integral or may be separately formed and after that coupled together.
The ceramic material making the discharge lamp may be sapphire, aluminium oxide (Al2O3), yttrium aluminium garnet (YAG), yttrium oxide (YOx), or aluminium nitride (AlN) which has a translucency and a heat-resistivity.
The term xe2x80x9ctranslucencyxe2x80x9d means an optical permeability in an order or penetrating outside a light generated by a discharge. Thus, it may not be restricted to be transparent, but may be diffusible. Although the swollen portion must be translucent, the cylindrical portions may simply have a light blocking effect.
In order to make the high-pressure discharge lamp compact, it is favorable that the internal volume of the discharge vessel is 0.06 cc or less, and more favorably it is 0.04 cc or less. It is favorable that the overall length of the discharge vessel is 35 mm or less, and more favorably it is in the range of 10-30 mm.
The metal tube is made of high melting point metal such as Molybdenum or Tungsten, which has a high corrosion resistance against the ionizing filling, and a high adhesiveness with the ceramics.
The metal tube is fixed to the inner surface or the outer surface of the cylindrical portion through a cermet, or a combination of cermet and sealing compound for ceramics. The fusible metal plug is plugged in the open end of the cylindrical portion after the ionizing filling has been filled in the discharge vessel. An electrode system is supported on the inner end of the fusible metal plug so as that an electrode formed on the end of the electrode system faces the interior of the swollen portion.
Fusible metals, such as platinum (melting point; 1772xc2x0 C.), vanadium (melting point; 1980xc2x0 C.) or Molybdenum (melting point; 2610xc2x0 C.) which has a thermal expansion coefficient close to that of the metal tube or any alloy with either one of those can be used for the fusing metal plug. When the metal tube is made of Molybdenum and the open end is closed by fusing the end portion, the metal tube can also serve as the fusing metal plug.
The fusion of the fusible metal plug is carried out by applying a high-power energy of such a YAG laser, a CO2 laser or an electron beam.
In case of that the metal tube is fit on the inner surface of the cylindrical portion, if the ratio BD/PL, of the maximum inner diameter BD of the discharge vessel to tho distance PL between the center of the discharge vessel and the inner end of the metal tube is in the range of 0.5-1.5, the efficiency of the discharge lamp will increase. And also, leaks caused by the exfoliation or the metal tube from the cylindrical portion can be prevented.
That is, the ratio BD/PL less than 0.5 are unfavorable, since it causes the temperature of the coldest portion to lower and thus decreasing the lighting efficiency. On the other hand, the ratio BD/PL in excess of 1.5 also unfavorable, since it causes an excessive temperature rise in the scaling portion, and thus causing leaks in the sealing portion.
In each electrode system, the electrode provided on the tip end of the electrode rod faces the interior of the discharge vessel. While the electrode rod is fixed to the fusible metal plug by being the other end of the electrode rod embedded or welded to the fusible metal plug.
The electrode rod is made of high melting point metal such as Tungsten, doped-Tungsten, Tungsten containing rhenium, or Molybdenum. The electrode is formed in a shape of coil wound on the tip end or the electrode rod. It is permissible that the electrode rod itself serves as the electrode. It is also permissible that the pair of electrode systems may be either of symmetrical or asymmetrical in their shape or size.
The ionizing filling contains luminous-metal gas, ramp voltage regulating gas and starting gas and buffer gas. For the luminous-metal gas and the ramp voltage regulating gas, metal halide made or one or more elements selected from sodium, lithium, scandium, rare earth metal, mercury or amalgam are used. The starting gas and/or the buffer gas are made of any one or a combination of rare gases such as xenon, argon, krypton and neon, and filled in the discharge vessel to exhibit a pressure more than one atmospheric pressure during lighting.
In the present invention, the starting voltage can be reduced by placing a starting-aid conductor, as needed.
The high-pressure discharge lamp according to the present invention is able to be lighted in a state that the translucent ceramic discharge vessel is exposed into air. The high-pressure discharge lamp can be formed in a double-bulb type lamp or a multiple-bulb type lamp wherein the ceramic discharge vessel is enclosed in a jacket tube made of translucent and heat-resistive hard glass such as quartz glass or borosilicate glass.
Furthermore, getters, such as Zr-aluminum alloy which makes the inside of the jacket bulb clean, can be provided on feeders etc. in the jacket bulb.
In a high-pressure discharge lamps according to one aspect of the invention a discharge vessel is formed in the swollen portion and the pair of cylindrical portions, and a high-pressure discharge lamp according to the present invention is supporting an electrode system while sealing a discharge vessel with a fusible metal plug inserted in an outside end of a metal tube joined to each cylindrical portion.
When the ratio T/D of the height T concerning the fusible metal plug and the diameter D of the cylindrical portion is in the range of 0.40-0.95, leaks taking place by exfoliation due to the thermal-expansion coefficient difference of the fusible metal plug and the metal tube, or voids leaks by voids taking place in the fusible metal plug decreases. Therefore the shortening of lamp life can be restraint.
If the ratio T/D is less than 0.4, voids taking place in the fusible metal plug by any reason communicate each other. Thus there arises a fear of that leaks take place. Moreover, if the ratio T/D is in excess of 0.95, and the surrounding height T may become too high, and ratio T/D may produce exfoliation by thermal-expansion coefficient difference with a metal tube increases. Since the heat capacity becomes large and thus the temperature of a fusible metal plug becomes difficult to rise, the fusible metal plug and the metal tube cannot be sufficiently welded together and thus cause a leaks from the interface between them.
As described above, a high-pressure discharge lamp according to one aspect of the invention can repress cracks generated in the once-fused portion of fusible metal plug and a metal tube due to degradation of a fusible metal plug by erosion of ionizing filling such as halide filled in the discharge vessel, and thermal shock at the time of turning ON or OFF the lamp by specifying the ratio T/D of the height T concerning the fusible metal plug and the outer diameter D.
A high-pressure discharge lamp according to another aspect of the invention is characterized by that the metal tube is principally made of high melting point metal such as Tungsten or Molybdenum.
Since Molybdenum and Tungsten have high corrosion resistance against ionizing filling and a thermal expansion coefficient close to that of the translucent ceramic discharge vessel, the discharge lamp according to this aspect of the invention is able to achieve the same effect as that achieved by the above-mentioned high-pressure discharge lamp.
The metal tube is fixed to the inner surface or the outer surface of the cylindrical portion through a cermet, or a combination of cermet and sealing compound for ceramics. The fusible metal plug is plugged in the open end of the cylindrical portion after the ionizing filling has been filled in the discharge vessel. Then the electrode on the electrode system is positioned in the discharge vessel by being suspended to the fusible metal plug.
A high-pressure discharge lamp according to still another aspect of the invention is characterized by that the diameter D is in the range 0.6-1.6 mm.
If the diameter D of the metal tube is less than 0.6 mm, and accordingly the electrode rod becomes thinner, there arises a fear of causing an excessive temperature rise in the electrode. If the diameter D or the metal tube is in excess of 1.6 mm, the wall-thickness of the cylindrical portion becomes thinner in relative to the diameter of the cylindrical portion at the portion around the metal tube. Then the strength of the cylindrical portion falls off. Thus there arises a problem that cracks take place in the cylindrical portion.
A high-pressure discharge lamp according to still another aspect of the invention is characterized by that the height T concerning the fusible metal plug is in the range of 0.24-1.5 mm.
If the height T concerning the fusible metal plug is less than 0.24 mm, the fusible metal plug cannot withstand a pressure rise in the discharge vessel at the time of turning ON the lamp. Then there arises a fear of causing leak through the damaged fusible metal plug. If the height T concerning the fusible metal plug is in excess of 1.5 mm, the heat capacity of the fusible metal plug increases therewith. Then an amount of heat required for fusing the fusible metal plug also increases. Thus there arises a problem that cracks tend to take place.
Here, a distance that a fused part of the fusible metal plug flows down is small, since the diameter of the metal tube is relatively small. Then the flowing-down distance is almost uniform in the circumferential direction. That is, the dispersion of the flowing-down distance is small. Thus the measurement of the height T concerning the fusible metal plug is easily carried out. However, if the dispersion of the flowing-down distance is large, it is able to adopt an intermediate value of the dispersed values of the flowing-down distance.
A high-pressure discharge lamp according to still another aspect of the invention is characterized by that the fusible metal plug is principally made of fusible metal such as Platinum, Vanadium or Molybdenum.
Even if a thermal-expansion coefficient difference with a tube ingredient is little by choosing a fusible metal plug which blockades an open end of a metal tube from a fusible metal which makes platinum, vanadium, or Molybdenum a principal component as mentioned above, and it receives a thermal shock, it can repress that exfoliation arises in both interface.
These fusible metals should just be in a ratio T/D of the height T concerning the fusible metal plug after solidification and the outer diameter D of a metal tube was indicated to be by the claim 1, although flowing-down distance of a fusible metal fused since each melting point differs from other.
A high-pressure discharge lamp according to still another aspect of the invention is characterized by farther comprising a heat-resistive and translucent jacket bulb enclosing therein the translucent ceramic discharge vessel sealed with the metal tube and the fusible metal plug.
According to this high-pressure discharge lamp further comprising the jacket bulb, an oxidization of elements in the translucent ceramic discharge vessel whose temperatures particularly rises during lighting of the lamp or a corruption of the translucent ceramic discharge vessel can be prevented. Thereby the handleability and the safety of the discharge lamp can be extensively improved.
Moreover, by providing a reflecting layer, a coloring film, a phosphor film, etc. on the jacket bulb, a lighting efficiency of the discharge lamp can also be improved. Thereby the discharge lamp can be used for various purposes.
A luminaire according to still another aspect of the invention comprises the high-pressure discharge lamp defined in any one of preceding aspects, a luminaire main-body mounting thereon the high-pressure discharge lamp, a lighting circuit equipped in the luminaire main-body for lighting the high-pressure discharge lamp.
Here, in this application, the term xe2x80x9cluminairexe2x80x9d has a wide concept containing all of such devices using lights radiated by high-pressure discharge lamps for any purpose. For example, the luminaire according to this aspect of invention is able to be applied for incandescent-lamp shaped high-pressure discharge lamps, lighting equipment, mobile-use head-lights, optical fiber-use light sources, image projectors, photo-chemical devices, fingerprint discriminators, etc.
Here, the term xe2x80x9cluminaire main-bodyxe2x80x9d means reminders of the luminaire from that the high-pressure discharge lamp is removed. Here, the term xe2x80x9cincandescent-lamp shaped high-pressure discharge lampxe2x80x9d means a luminaire in which a high-pressure discharge lamp and a stabilizer thereof are integrated together, and a bulb-base is added thereto for receiving a commercial power. By loading the bulb-base to a corresponding lamp socket, this type of lamp device is used as if it is an incandescent lamp.
The luminaire can be equipped with light-governors, such as lenses, filters, optical diffusion covers, etc. for governing and protecting the light intensity and light distribution of the discharge lamps, reflectors or housings.
The luminaire main-body and the lighting circuit may be formed in integral, or may be formed separately.
The lighting circuit may be either of a high frequency AC type, low frequency AC type or a DC type.
Additional objects and advantages of the present invention will be apparent to persons skilled in the art from a study of the following description and the accompanying drawings, which are hereby incorporated in and constitute a portion of this specification.